class WalkKernel
{
public:
    virtual double Evaluate(const Walk &w0, const Walk &w1) const = 0;
};

class WalkKernelSimple : public WalkKernel
{
public:
    void SetParameters(const NodeKernel &nodeKernel, const EdgeKernel &edgeKernel);
    
    double Evaluate(const Walk &w0, const Walk &w1) const;

private:
    const NodeKernel *_nKernel;
    const EdgeKernel *_eKernel;
};